This invention relates to sulfur-containing fertilizer and, more particularly, to a process for the manufacture of homogeneous, particulate, urea sulfur fertilizer.
Sulfur-containing fertilizers are in ever larger demand for compensating sulfur deficiencies in the soil. Conventionally, sulfur has been applied in the form of elemental sulfur, ammonium sulfate, ammonium bisulfate, sulfides or gypsum, or in combination with other fertilizer materials such as urea. A urea sulfur product having a 40-0-0-10(S) grade was marketed for a period of time while, more recently, a sulfur coated urea has been produced.
According to Canadian Pat. No. 634,902, which issued Jan. 16, 1962 to F. A. Horsley, et al., molten urea and molten sulfur are mixed by passing molten urea and molten sulfur through a pump and the resulting mixture is fed through a tank provided with agitation into a prilling tower. Vigorous stirring is necessary to avoid phase separation. Instead of employing a prilling tower, the product may be made by other techniques such as by granulating, spherodizing or flaking. The main disadvantage of the sulfur urea product made according to these methods is that the elemental sulfur does not oxidize rapidly enough to provide nutrient sulfur that is available early in the growing season, the sulfur becoming available only in the later stages of plant growth.
According to U.S. Pat. No. 3,903,333, which issued Sept. 2, 1975 to A. R. Shirley Jr., et al., urea is coated with layers of sulfur in a rotary coating drum to produce a sulfur-coated urea. The sulfur-coated urea made according to this disclosure may be considered a slow-release fertilizer which releases both its nutrients very slowly over a long period of time. The sulfur of sulfur-coated urea does not usually become available until one year after application.
It would, therefore, be advantageous to have a sulfur-containing fertilizer which has not only a high nutrient content but also contains its sulfur in a form that is more readily and quickly available as a plant nutrient. Such a fertilizer can be applied and be effective early in the growing season, or at other times, for example, when a rapid response to the nutrients is desired.